The following document lists the file abstract/PCOX_HELIX_2.abs
from catalogue VI/111.
A plain copy of the file
(without headers/trailers) may be downloaded.
The Helix nebula (NGC 7293) is the closest planetary nebula with a massive envelope of molecular gas (130 pc). It is far larger in angular size than any other of this class, and offers the best opportunity to explore the large and small scale structure of a planetary nebula in great detail. In the open time program (COX_2), we proposed a comprehensive study of the distribution of the infrared emission in the Helix nebula by using ISOCAM, PHOT and the LWS. The results have proven to be spectacular and provide the first basis of a detailed study of the dust associated with the small neutral globules in the nebula and even the previously ejected, outer shell (Cox et al. in preparation). We propose to follow-up these ISO results to investigate at the highest possible angular resolution provided by ISO the small scale structure of the infrared emission associated with the molecular envelope of the Helix nebula. The field selected includes the two fields recently observed with the Hubble Space Telescope. Furthermore, we propose to investigate the spectral properties of the mid-infrared emission in the neutral and the ionized regions of the nebula using the ISOCAM CVF. This will enable to study the excitation through the ionic lines and to probe the changes in the dust populations across the ionized-neutral interface by following the spectroscopic changes in the dust emission bands and the behaviour of the continuum. Such observations are fundamental for understanding the physical conditions in the envelopes of planetary nebulae and will provide, at unmatched linear resolution, detailed insights into basic processes which are of general importance in the interstellar medium.